Several patents and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents and publications is incorporated by reference herein.
Glass laminated products have contributed to society for almost a century. Beyond the well known, every day automotive safety glass used in windshields, laminated glass is used as windows for trains, airplanes, ships, and nearly every other mode of transportation. Safety glass is characterized by high impact and penetration resistance and does not scatter glass shards and debris when shattered.
Safety glass typically consists of a sandwich of two glass sheets or panels bonded together with an interlayer of a polymeric film or sheet, which is placed between the two glass sheets. One or both of the glass sheets may be replaced with optically clear rigid polymeric sheets, such as sheets of polycarbonate materials. Safety glass has further evolved to include multiple layers of glass and polymeric sheets bonded together with interlayers of polymeric films or sheets.
A more recent trend has been the use of glass-laminated products in the construction of homes and office structures. The use of architectural glass has expanded rapidly over the years as designers incorporated more glass surfaces into buildings. Threat resistance has become an ever-increasing requirement for architectural glass laminated products. These newer products are designed to resist both natural and man-made disasters. Examples of these needs include the recent developments of hurricane resistant glass, now mandated in hurricane susceptible areas, theft resistant glazings, and the more recent blast resistant glass-laminated products designed to protect buildings and their occupants. Some of these products have great enough strength to resist intrusion even after the glass laminate has been broken. For example, when a glass laminate is subjected to high force winds and impacts of flying debris as occur in a hurricane or where there are repeated impacts on a window by a criminal attempting to break into a vehicle or structure.
Society continues to demand more functionality from laminated glass products beyond the safety characteristics described above. One area of need is to reduce the energy consumption within the structure, such as an automobile or building to which the laminated glass is applied. The sun's energy strikes the earth over a wide spectral range from 350 nm to 2,100 nm. Nearly half the energy is within the near infrared region of 750 nm to 2,100 nm. Removing the energy from the visible region would sacrifice visual transparency through windows and, therefore, detract from one of the advantages of windows. However, since the human eye does not sense the near infrared region, attempts have been made to prevent the transmission of the energy from the near infrared region through glass laminates by modifying the glass and/or the polymeric interlayer, by the addition of further layers or combinations thereof.
Liquid crystals are known to appear in many different forms, including the smectic, nematic and twisted nematic (or cholesteric or chiral nematic) forms. A comprehensive description of the structure of liquid crystals in general, and twisted nematic liquid crystals in particular is given in “The Physics of Liquid Crystals,” P. G. de Gennes and J. Prost, Oxford University Press, 1995. Twisted nematic liquid crystalline materials are also disclosed in, for example; U.S. Pat. Nos. 3,679,290, 4,637,896, 6,300,454, 6,417,902 and 6,486,338 references disclosed therein. The chirality of the liquid crystalline material determines the existence of twisted nematic phases. The presence of a chiral moiety within the liquid crystalline material induces the existence of twisted nematic phases.
Liquid crystalline materials have been considered for use in glazings to control solar radiation. Devices that incorporate micellar liquid crystal materials (discrete particles of liquid crystal materials), within matrix materials generally exhibit haze at unacceptable levels for a transparent glazing. Continuous coatings and films of liquid crystalline materials (nonmicellar liquid crystalline materials), have been disclosed in U.S. Pat. Nos. 3,679,290; 5,731,886; 5,506,704; 5,793,456; 6,831,720; 6,630,974; 6,661,486; 6,710,823; 6,656,543; and 6,800,337. Liquid crystalline materials have also been used in window glazing units, as described in U.S. Pat. Nos. 5,156,452; 5,285,299; 5,940,150; 6,072,549; 6,369,868; 6,473,143; and 6,633,354, for example.
It is desirable to have a composition that reduces the transmission of near infrared radiation and that can be used in a low-haze glazing unit that is also an effective safety glass unit.